A review of the mechanism of impulse voltage generation on the secondary busbar of electromagnetic transmitter

Author： GOZ Electric Time：2024-08-22 09:28:22 Read：11

    Electromagnetic detection is the main method for marine oil and gas resource exploration, and the marine electromagnetic transmitter is the key equipment of the marine electromagnetic detection system. At present, when the underwater towed body of the marine electromagnetic transmitter works for a long time, the switch device will be damaged. Firstly, the transmitting bridge commutation process using a unidirectional controllable source circuit is analyzed, and it is found that the parasitic inductance feedback energy of the transmitting dipole causes the secondary bus to generate an impulse voltage, which increases the voltage stress of the switch tube. Then, the working mode of the bidirectional controllable source circuit is analyzed, and a dual-variable decoupling control strategy is proposed. Based on the model established before and after the transformer, the original coupled nonlinear system is globally linearized into two single-input single-output systems, so as to obtain the functional relationship of the sliding mode controller. The simulation and experimental results show that the designed controllable source circuit can significantly reduce the impulse voltage of the bus capacitor and the voltage stress of the switch tube, and improve the dynamic performance and efficiency of the system.

    Keywords: electromagnetic transmitter; bidirectional controllable source circuit; impulse voltage; decoupling control

    Among geophysical geological exploration methods, marine electromagnetic exploration is based on the differences in the polarizability and conductivity of various gas and liquid resources, rocks and ores, and observes their electromagnetic fields to achieve effective detection of the target. For example, the oil and gas structure is characterized by high resistivity, while the seabed bottom layer filled with salt water has good conductivity. In the 20th century, the oil and gas industry spent hundreds of millions of dollars each year using traditional methods such as drilling to find offshore hydrocarbons. Today, electromagnetic detection systems are considered part of the standard toolkit for studying offshore geology. At present, domestic marine electromagnetic transmitters have good exploration results for oil and gas resources within 1000m, but for deep resources, there are still many technical problems to be solved in terms of power, frequency, and method and technical accuracy detection of electromagnetic transmitters.

    Marine controllable source electromagnetic transmitters are the core equipment of marine electromagnetic detection systems. However, at present, almost all of my country's large-scale sea area geophysical exploration equipment relies on imports, which seriously affects the development of new technologies for electromagnetic detection of deep resources in my country. Therefore, it is crucial to have my country's own intellectual property rights for seabed geophysical detection equipment and master its core technology. The TXM-22 transmitter of Germany's etronix company uses uncontrolled rectification technology and has high output power. The output voltage is adjusted by adjusting the excitation current of the generator. The manufacturing of the generator is relatively complex and the volume and mass are large. The GGT-30 transmitter developed by Zonge Company in the United States uses phase-controlled rectification technology to design a controllable source circuit, and controls the output voltage by controlling the trigger angle. When the trigger angle is large, it will lead to a low power factor. In addition, Phoenix Company in Canada uses pulse width modulation (PWM) conversion to design the TXU-30 transmitter.

    For land electromagnetic transmitters, the relevant literature introduces the influence of the electromagnetic transmitter dipole inductance on the edge steepness of the transmitting current. The relevant literature proposes to use an absorption circuit to reduce the shutdown time, but does not mention the influence of the dipole inductance energy storage on the bus voltage. When the marine electromagnetic transmitter tow body works underwater for a long time, it will cause damage to the switch tube. According to the introduction in the relevant literature, the transmitting dipole has a parasitic inductance of 500uH. If the influence of this inductance is ignored, when the transmitting bridge is commutated, the induced voltage generated will damage the equipment. The energy fed back on the inductor is absorbed by the capacitor slot. This method requires increasing the bus capacitance and increasing the circuit volume. Due to the limited volume of the underwater tow body, it is not feasible, especially for high-power electromagnetic transmitters.

    The dual-active full bridge (DAB) DC-DC converter has a symmetrical structure, can realize bidirectional energy flow, and has the characteristics of high power density and electrical isolation, and is widely used. Its control methods include single-phase-shift (SPS) control, dual-phase-shift (SPS) control, and dual-phase-shift (SPS) control. DPS) control, extended-phase-shift (EPS) control, triple-phase-shift (TPS) control. In different control methods, the control algorithm is basically designed with the inductor current stress, return power, and soft switching range as the optimization targets. The DAB converter is essentially a multi-input multi-output (MIMO) system, and the internal variables are coupled to each other in the output characteristics to fully describe it. In recent years, nonlinear control methods based on differential geometry have provided a solution for the decoupling of MIMO systems. It uses the system's inductor current and bus voltage as feedback control quantities, compares the given value and the feedback value to obtain the error signal, and constructs a switching function with the error and the integral value of the error, and then designs the sliding mode control law of the system to obtain the functional relationship of the sliding mode controller. In addition to being able to control current stress and bus voltage, this output feedback sliding mode control strategy can also improve the anti-disturbance capability of the system.

    Through the analysis of the commutation process of the transmitting bridge, it is known that the energy feedback of the dipole inductor causes the busbar to generate an impulse voltage, which increases the voltage stress of the switch tube and causes the switch tube to be damaged when working for a long time. A bidirectional controlled source circuit is proposed. Aiming at the problem that the control variables of the bidirectional controlled source circuit cannot be completely decoupled and the power is limited, a sliding mode control method based on state feedback precise linearization is proposed. The dynamic phasor method and the fundamental wave approximation method are used to establish the average phasor model of the front and rear stages of the transformer for the bidirectional controlled source circuit of the general load, and the range of the feedback control law parameters is obtained by analyzing the closed-loop error dynamic equation of the system, which provides a theoretical basis for parameter selection. The simulation and experimental results show that the control method can realize soft switching in the whole process of the experiment, which greatly improves the efficiency and dynamics of the transmitter controlled source circuit.